I have a 83... 355 SBC Vortec heads, 10;1 comp, summit k1103 cam, Edelbrock intake, q-jet, dialed in. I have heddman 1 5/8 primary's to a 2.5" collector, to a 3" o.d into a catco high flow cat 3" to a Ravin cross flow muffler, and 2 x 2.5 tailpipes.....

I found out that the 3" High flow catco cat only flows at 299 cfm.
and according to them a 3" pipe flows at 408 cfm.
http://www.smb.net.au/catalyticconverters.htm

There are several references on this site and others for in and out muffler flow ratings but I haven't been able to find any ratings for cross flow mufflers.
I love the sound of the Ravin but not sure how well it flows?
I have read both good and bad about it.

According to research I have done my motor should be an honest 330 - 350 hp at the flywheel. I have seen that most suggest a approx. flow value of 2.2 cfm per HP on the exhaust side. So if this is correct I would need say 330hp x 2.2 = 726 cfm flow for the exhaust? I realize that some back pressure is needed but 2.2 seems to be a ball park figure.

According to this research my exhaust is choking my motor.
I can see why people are going to true duals or 4" systems.
Not knowing what my muffler flow rating is ?
(if anyone does please let me know)
I think I would see an advantage in removing the cat? 25% More flow.

Not to create another It's against the law to remove your cat thread, I'm just curious if people with similar engine combo's to mine have seen an increase in power by removing the cat ( I read many posts with the stock 305, 350 cars saying there is no advantage) but I`m talking about a mild performance motor seeing an advantage?

Thoughts Gentlemen?

 

i honestly think you can pick up some HP removing the cat even on a mild tune motor. I would just have your exhaust guy make you a straight through pipe at the cat and have it flanged that way come inspection time just put your cat back on.

 

From what I can see, and figure I agree..... I'm going to try a 3" pipe straight through the cat. I will weld and alter it myself. I'm sure I will see a gain in performance across the rpm range. I have contemplated a cat delete with 3.5 O.D. piping from the 2.5 collectors. I would have to modify the muffler to accept the 3.5 inlet, then out to the 2.5 tail pipes.

Still interested to know what the Ravin or any other crossflow mufflers are rated at though......

 

a high flow cat doesnt eat much power at all, you shouldnt notice it, unless its clogged. The car may sound different, giving you a placebo effect of more performance, but its really not. the cars exhaust will stock more with out a cat too. main reason i put cats back on my car.

as for the pipes, even if the 3" pipe flows 408cfm, does the engine produce 408cfm of exhaust? probably not, so again, the smaller 299cfm rating of the cat may not be all that "bad"

and taking off the cat is illegal, blah blah blah...

 

Here is my point....The link I posted about the 299 CFM for a catco high flow cat isn't anywhere enough to support a 330 hp motor. (http://www.smb.net.au/catalyticconverters.htm) They say on the site the testing wasn't done on a certified machine, however it still shows a ball park. I know everything on the net is true right ? lol

On this site http://www.exhaustvideos.com/faq/how...pipe-diameter/ they talk in simplified math about how to calculate what is required for the engine to have correct exhaust. The 2.2 cfm per Hp is what they suggest. If you look down to the area titled "quick and dirty exhaust system math" they explain. There is a nice table there that states a 3" exhaust ( straight pipe) flows at 747 cfm. So a cat converter that only flows 299 cfm will obviously be very restrictive in the system.

My concern is to replace the cat with straight pipe only to find my Ravin muffler only flows a little better or maybe less than the cat converter? I haven't seen any flow numbers for this muffler or any cross flow muffler...